A precursor strategy is a system by which a single precursor is used to manufacture a variety of different products. The use of a precursor strategy is quite common in synthetic organic chemistry.
As used herein, a precursor is a molecule capable of reacting with different compounds, such as modifiers, to produce a number of different products. A precursor molecule comprises a core and one or more reactive moieties. The "core" is the part of the compound that does not generally change and the part that often, but not necessarily, possesses some specific properties critical for the desired application. Thus, the core is generally untouched upon reaction with a modifier.
A "reactive moiety" is a group that reacts in a highly effective, preferably quantitative, and specific manner with a particular modifier to form a particular product or with a mixture of modifiers to form a pool of products. If a core part of a precursor contains some functionalities that are also capable of reacting with the modifier, these functionalities must be protected.
A precursor strategy will work successfully only if some demands are fulfilled. These demands include the following:
1. If a precursor is a complex molecule and is prepared by multi-step synthesis, the precursor reactive moiety or moieties must be stable in all conditions used during the synthesis after its introduction. However, this rule is not applicable if a reactive moiety is introduced at the very last step of the precursor synthesis. PA1 2. It is highly desirable for the yield of the reaction between a precursor reactive moiety and a modifier to be close to quantitative. This is especially important when the precursor contains more than one reactive moiety. PA1 3. The core part of a precursor must be stable in the conditions of transformation, that is, the conditions under which the precursor reacts with a modifier. PA1 4. One or more a modified site, that is, parts of a product molecule that are formed after reaction between a precursor reactive moiety and a modifier, must tolerate the deprotection conditions if a deprotection step is necessary to prepare a desired product. PA1 5. It is desirable for the transformation time to be relatively short. PA1 reacting a first compound containing a first moiety selected from the group consisting of --COCOOCR.sub.3, --COCR.sub.2 CR.sub.2 CO--, --COCR.dbd.CRCO-- and --COSSCO-- with a second compound containing a primary or secondary amine, which may or may not be an amino substituted nucleoside or nucleotide, to form a third compound containing a second moiety selected from the group consisting of --NRCOCOOCR.sub.3, ##STR1## said first moiety attaching to a nitrogen of the amine to form said second moiety, wherein each R independently represents H or a substituted or unsubstituted alkyl group; PA1 reacting a protonated nucleophile (HNu) with the second moiety of said third compound to form a fourth compound containing a third moiety selected from the group consisting of: --NRCOCONu, --NHCOCR.sub.2 CR.sub.2 CONu, --NHCOCR.dbd.CRCONu and --NHCOSSCONu. PA1 reacting a compound containing a first moiety selected from the group consisting of --COCOOCR.sub.3, --COCR.sub.2 CR.sub.2 CO--, --COCR.dbd.CRCO-- and --COSSCO-- with a first monomer containing a primary or secondary amine, which may or may not be an amino substituted nucleoside or nucleotide, to form a second monomer containing a second moiety selected from the group consisting of --NRCOCOOCR.sub.3, ##STR2## said first moiety attaching to a nitrogen of the amine to form said second moiety, wherein each R independently represents H or a substituted or unsubstituted alkyl group; PA1 reacting said second monomer with at least one other monomer to form an oligomer or polymer; PA1 reacting a protonated nucleophile (HNu) with the second moiety to form a third moiety in said oligomer or polymer, said third moiety being selected from the group consisting of: --NRCOCONu, --NHCOCR.sub.2 CR.sub.2 CONu, --NHCOCR.dbd.CRCONu and --NHCOSSCONu.
Oligonucleotides bearing various functionalities have become common place tools in molecular biology and diagnostics. Goodchild, J., "Conjugates of Oligonucleotides and Modified Oligonucleotides: A Review of Their Synthesis and Properties," Perspectives in Bioconjugate Chemistry, pp. 77-99 (1993). One of the most efficient routes to the synthesis of functionally modified oligonucleotides (FMOs) is the introduction of a precursor, that is, a nucleotide monomer bearing a reactive moiety, into the oligonucleotide. At the end of solid phase synthesis, the precursor reacts with a desired linker or modifier. This strategy enables one to synthesize a wide variety of FMOs from a single parent oligonucleotide.
MacMillan, A. and Verdine, G., "Engineering Tethered DNA Molecules by the Convertible Nucleoside Approach," Tetrahedron, 47: 2603-2619 (1991), and Ferenz, A. and Verdine, G., "Aminolysis of 2'-Deoxyinosine Aryl Ethers: Nucleoside Model Studies for the Synthesis of Functionally Tethered Oligonucleotides," Nucleosides & Nucleotides, 11: 1749-1763 (1992), have elaborated a convertible nucleoside strategy to prepare functionally tethered oligonucleotides (FTOs). This convergent strategy is based on the use of O-substituted deoxyuridine and deoxyinosine as convertible nucleosides. Upon treatment with aqueous amines, precursor oligonucleotides containing convertible nucleosides undergoes a transformation giving rise to a FTO.
Buhr et al., U.S. Pat. No. 5,466,786, described the incorporation of a 2'-deoxy-2'-O-(ethoxycarbonylmethyl)-cytidine into an oligonucleotide. After solid phase synthesis and deprotection, the ester group, which is a reactive moiety, can be hydrolyzed to a carboxy group by treatment with NaOH or derivatized to an amide or substituted amide by a reaction with NH.sub.3 or a primary aliphatic amine.
Hebert et al., Tetrahedron Letters, 35: 9509-9512 (1994), reported the N-acylation of a DMT-hydroxymethylpyrrolidinol precursor with a number of carboxylic acids. N-substituted DMT-hydroxymethylpyrrolidinols were further phosphitilated and used for the preparation of phosphodiester oligomer combinatorial libraries.